What is the compressed form of an IPv6 address?

RFC 5952 defines the canonical short form: leading zeros in each group are removed and the single longest run of consecutive zero groups is replaced with a double colon (::). For example 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1.

Why would I need the expanded form?

Sorting, database storage, firewall rules and PTR record generation often need the full 8-group, 39-character notation, because string comparison only works when every address has the same length.

Is my address sent to a server?

No. The conversion runs entirely in your browser with JavaScript. Nothing you type in this tool leaves your device.

IPv6 Compress & Expand

IPv6 address

That does not look like a valid IPv6 address.

Compressed (RFC 5952)

Expanded (full notation)

Reverse DNS zone (ip6.arpa)

Why IPv6 addresses have two notations

A full IPv6 address is eight groups of four hexadecimal digits, 39 characters in total. Because most real addresses contain long runs of zeros, RFC 5952 defines a canonical short form: leading zeros are dropped from each group and the single longest run of zero groups collapses into a double colon. Both notations refer to exactly the same address.

The expanded form matters whenever addresses are compared as text: database keys, log analysis, firewall rule sets and PTR record generation all rely on every address having identical length. The compressed form is what you use in configuration files, URLs and documentation.

What this tool handles

Standard addresses, IPv4-mapped addresses like ::ffff:192.0.2.128, and zone indexes like fe80::1%eth0 (the zone is preserved but excluded from conversion). The reverse DNS name is generated from the expanded form by reversing all 32 nibbles and appending ip6.arpa, which is what you put in PTR records.

Everything runs in your browser. If you want registration and geolocation data for an address instead, use the IP Lookup.